1. Technical Field
This invention concerns materials which can serve as intermediate agents for transfer of heat from an energy source to a load object. More specifically, it relates to particulate compositions of matter which can be used effectively for heating or cooling applications.
In a typical heating application, agent B receives heat from source A and delivers its heat to load object C. The same applies, in principle, to a cooling application. In that case, agent B receives cold (gives up its heat to) source A and gives up its cold (receives heat from) load object C. Putting it in another way, one may consider the load object of cold as a source of heat and the source of cold as the load object of heat. Thus, intermediate agents play a similar role in heating and cooling.
2. Description of Prior Art
Examples of common heating and cooling applications come to mind quite readily. Electric corn poppers or hairdryers use air as the intermediate heating agent. Pressing irons or frying pans use metal as intermediate heating agents. Hot oil is used as an intermediate heating agent in deep frying and water is used as the primary intermediate heating agent in most cooking applications. Turning to a common example of cooling, air is the primary cooling intermediate in a refrigerator. All of the above are instances of dynamic, steady-state heat transfer, where the intermediate agents receive and discharge heat concurrently, either intermittently or continuously. Under these conditions, the agents' ability to transfer heat is of primary importance.
In other situations, the process of heat transfer is sequential rather than concurrent. In such cases, an intermediate heating (cooling) agent receives heat (cold) from a source, stores the heat (cold) for later use and then delivers it to a load object, likely at another location away from the original source. Sequential heating is exemplified by preheated water in a jacketed baby feeding dish or in a hot water bottle. A freezer pack is an example of stored cold. It is clear that in sequential heating/cooling applications the intermediate agents' ability to store heat is an important attribute. Measures of capacity to store heat for materials which do not undergo a change of state relate to specific heat per unit weight and, in combination with density, specific heat per unit volume. Changes of state will be considered later.
One other attribute worthy of mention is fluidity; i.e. the agents' ability to flow readily and surround the load object, thereby delivering heat to more than one surface. It can, and often does, play an important role in concurrent as well as sequential schemes of heat transfer, as will become more evident in the discussion which follows.
Against this background, one can assess the ability of various materials, in their respective physical states, to act as intermediate heat transfer agents.